Various types of valuable document validators for use in automatic transaction machines, such as vending or gaming machines, are well known. Typically, a consumer inserts coins and bills into such vending machines in order to purchase a product or service. Currency acceptors receive currency, for example paper money or coins, and perform various authenticity and denomination tests, and then either accept the tendered currency as valid or reject the currency and return it to the consumer. When accepted as genuine currency, the bill or coin is usually transported to a currency storage assembly, for example a cashbox or coin tube, where it is stored and a selected item is vended along with any change that may be due.
Thieves have been known to attempt to cheat vending machines to receive products or services without actually paying for them. Often, thieves fool currency acceptors with things that would not fool humans. For example, a thief may attach a string-like member, or any object capable of creating a tail, to a bill and then manipulating the tail to retrieve the bill after it has been accepted by a bill validator. This type of fraud is commonly known as “string-fraud.” Although areas containing automatic transaction machines, such as vending machines and gaming machines, are increasingly monitored by automatic video devices, the string-fraud technique can be difficult to detect during or after an occurrence because during normal operation of the machine genuine bills are returned to consumers if they cannot be validated due to wear or foreign matter. Moreover, it is a never-ending game between thieves and the developers of automatic transaction machines—as thieves develop new methods to overcome current anti-fraud methods and devices, new countermeasures must be developed.